The present invention relates to a photoelectric transducer apparatus for focus detection, and more particularly, to a photoelectric transducer apparatus which is capable of detecting a focussed condition even when brightness varies widely in a focus detector apparatus which detects a distance to an object being photographed in accordance with an amount of electric charge delivered by a self-scanning image sensor such as a CCD.
Recently, various improvements have been made in the field of focus detector apparatus and a required detectable range of brightness has been also extended. In particular, it is hoped to further widen a photometric range in the low brightness region. A method for obtaining a constant output over a wide range from a low to a high brightness is shown in Japanese Laid-Open Patent Application Sho 56/1981-154,880, for example, which monitors a change in potential of a storage electrode for storing a signal charge and transfers the signal charge to a transfer line when the potential reaches a given level. Another method is shown in Japanese Laid-Open Patent Application Sho 57/1982-64,711 in which a light detector for monitoring is disposed adjacent to an array of photoelectric transducers to control a time period for storing charge in a self-scanning photoelectric transducer portion in response to an amount of the stored charge in the light detector in accordance with the amount of incident light rays. Further method is shown in Japanese Laid-Open Patent Application Sho60/1085-121,409 in which a reset pulse generator is provided for resetting a transfer clock pulse generator in response to an output for decision when an output from a monitor circuit becomes lower than a given level and a shift pulse generator is connected to the reset pulse generator so as to produce a shift pulse in response to a reset pulse to respond to a wider range of brightness.
Of the above prior art examples, the disclosure of Japanese Laid-Open Patent Application Sho60/1985-121,409 eliminates an error caused by synchronizing a signal charge with a transfer clock pulse, especially an error in an integrating period in a high brightness. In this point, the Japanese Laid-Open patent application Sho60/1985-121,409 is more improved than the other Japanese Laid-Open patent applications Sho56/1981-154,880 and Sho57/1982-64,711. In the Japanese Laid-Open Patent Application Sho60/1985-121,409, however, it takes several tens of .mu.s until a signal charge is transferred to a transfer line after completion of an integration period has been detected and such time can not be accelerated any more. Consequently, there is a problem that a detectable range in a high brightness condition becomes narrow because an integration period in a high brightness becomes too small when a detectable sensitivity in a low brightness is raised.